Document Classes, the Preamble, and Packages

The document class determines the basic structure of the document; the preamble contains global settings; packages add capabilities to the document. The example below demonstrates how the three work together.

EasyLaTeX compiler setting: pdfLaTeX with the standard article class. The examples also use graphicx, xcolor, and hyperref.

Minimal Preamble#

The preamble is located after \documentclass and before \begin{document}:

\documentclass[a4paper,12pt]{article}

% Preamble: load packages and set global options

\begin{document}

This is the body.

\end{document}

The body contains the content to be displayed; the preamble specifies how the entire document works. Do not put \usepackage in the body.

Choosing a Document Class#

\documentclass The curly braces specify the document class, and the square brackets provide options:

\documentclass[a4paper,12pt]{article}

Do not switch to book in short articles just to get \chapter. A document class primarily expresses the type of document, and only secondarily the number of available commands.

Loading Packages#

Use \usepackage to load the functionality. The following three packages handle images, colors, and links, respectively:

\usepackage{graphicx} % \includegraphics
\usepackage{xcolor}   % \textcolor, \colorbox and other color commands
\usepackage{hyperref} % Clickable contents, references, and URL

Package names do not include the .sty suffix. Loading a package does not mean that you must use it immediately; the corresponding effects are produced only when its commands are invoked in the body.

Setting Document Information#

Title information is usually placed in the preamble, and then output in the body using \maketitle:

\title{Experiment Report}
\author{Alex Taylor}
\date{July 2026}

\begin{document}
\maketitle
\end{document}

Commands such as \title only store information and do not automatically typeset the title; only \maketitle generates the title area at the current location.

Define Your Own Commands#

Repeated phrases or formatting can be encapsulated as commands in the preamble:

\newcommand{\LaTeXdoc}{\LaTeX{} documents}

Use in the body:

This document introduces  \LaTeXdoc  and its basic writing workflow.

This is suitable for stable, repetitive content. Do not encapsulate all formatting in custom commands from the outset; extract it when repetition actually occurs, making the document easier to read and debug.

Loading Order and Boundaries#

• The document class must be the first LaTeX command in the file;

• Packages and global settings belong in the preamble;

• hyperref is usually placed after most packages to avoid overriding link settings;

• For the same functionality, prefer one default package setup and avoid loading overlapping alternatives simultaneously;

• Before modifying a template provided by a school, journal, or publisher, read the template comments first; do not arbitrarily delete its document class or existing packages.

Complete example#

\documentclass[a4paper,12pt]{article}

\usepackage{graphicx}
\usepackage{xcolor}
\usepackage[colorlinks=true,linkcolor=blue,urlcolor=blue]{hyperref}

\title{Preamble Example}
\author{Alex Taylor}
\date{\today}
\newcommand{\LaTeXdoc}{\LaTeX{} documents}

\begin{document}

\maketitle

This is an example of  \textcolor{blue}{\LaTeXdoc}.
\href{https://www.latex-project.org/}{LaTeX Project}  is the official LaTeX project website.

\end{document}